1. Field of the Invention
The present invention relates to a master cylinder, and more particularly, to a brake master cylinder for vehicles, in which channel and sealing structures are improved.
2. Description of Related Art
In general, a hydraulic brake system generates a braking force by transmitting hydraulic pressure, which is generated by stepping on a brake pedal, to hydraulic brakes installed on front and rear wheels. This hydraulic brake system includes a booster increasing force when the brake pedal is applied, a hydraulic fluid reservoir storing a hydraulic fluid for forming hydraulic pressure, and a master cylinder transferring the hydraulic pressure to wheel cylinders in cooperation with the booster.
FIG. 1 is a cross-sectional view illustrating a conventional master cylinder before braking. FIG. 2 is a cross-sectional view illustrating a conventional master cylinder during braking. FIG. 3 is an enlarged cross-sectional view illustrating an important part of FIG. 2.
As illustrated in FIGS. 1 and 2, the conventional master cylinder includes a cylinder 10 having a blind end and first and second pistons 20 and 30 housed in the cylinder 10. The first and second pistons 20 and 30 are spaced apart from each other so as to be able to make relative motion.
A first boosting force transmission member 18 is interposed between an output shaft of the booster and the first piston 20. A second boosting force transmission member 19 is interposed between the first piston 20 and the second piston 30.
At this time, a space between the first piston 20 and the second piston 30 and a space between the second piston 30 and the blind end of the cylinder 10 serve as a first hydraulic chamber 21 and a second hydraulic chamber 31, respectively. The first and second hydraulic chambers 21 and 31 are provided with respective return springs 40 for returning the first and second pistons 20 and 30.
Further, the cylinder 10 is provided with first and second inlets 22 and 32 feeding a fluid into the master cylinder, and first and second outlets 23 and 33 transferring the fluid pressurized at the first and second hydraulic chambers 21 and 31 to the wheel cylinders. The first and second inlets 22 and 32 are connected with an oil tank.
Meanwhile, the first and second pistons 20 and 30 are equipped with first and second inflow chambers 24 and 34 in intermediate portions thereof in which the fluid introduced into the cylinder 10 through the first and second inlets 22 and 32 is stored before it is sent to the first and second hydraulic chambers 21 and 31. The first and second pistons 20 and 30 are provided with communication holes 50 in leading ends thereof which connect the first and second inflow chambers 24 and 34 with the first and second hydraulic chambers 21 and 31.
The communication holes 50 have center valves 60 installed therein so as to interrupt or allow the fluid that flows through the communication holes 50 to thereby close or open the first and second hydraulic chambers 21 and 31.
Each center valve 60 includes a valve body 62 and a sealing member 61 fitted around a leading end of the valve body 62. Each of the communication holes 50, which hold the respective center valves 60, includes a large diameter passage 51 holding the sealing member 61, and a small diameter passage 52 holding the remaining valve body 62 other than the sealing member 61.
The fluid flows through each communication hole 50, particularly a gap between the center valve 60 and the communication hole 50. In contrast, when the sealing member 61 comes into contact with a valve seat 53 formed by transition from the large diameter passage 51 to the small diameter passage 52, the fluid does not flow through each communication hole 50. To this end, the sealing member 61 held in the large diameter passage 51 is formed so as to have an outer diameter that is smaller than an inner diameter of the large diameter passage 51 and is greater than an inner diameter of the small diameter passage 52. Further, the inner diameter of the small diameter passage 52 is formed so as to be greater than an outer diameter of the valve body 62 held in the small diameter passage 52.
Meanwhile, in the rear of the respective center valves 60, cylinder pins 70 pass through the first and second inflow chambers 24 and 34 and are fixed to the cylinder 10. An elastic member 64 is installed in the large diameter passage 51 of each communication hole 50 so as to elastically support the corresponding center valve 60 toward the corresponding cylinder pin 70. The center valves 60 allow or block the flow of fluid through the communication holes 50 by interaction of the cylinder pins 70 and the elastic members 64 and by forward or backward movement of the first and second pistons 20 and 30.
Now, the operation of the conventional master cylinder will be described in detail.
When the brake pedal is applied for breakage, the first boosting force transmission member 18 is pushed by the output shaft of the booster, and thus the first piston 20 moves forwards. Then, the second boosting force transmission member 19 is pushed in cooperation with the first piston 20, and thus the second piston 30 also moves toward the blind end of the cylinder 10.
As the first and second pistons 20 and 30 move forwards, the center valves 60 moves along with the first and second pistons 20 and 30. As a result, as in FIG. 2, the valve bodies 62 of the center valves 60 are separated from the respective cylinder pins 70.
Further, when the valve bodies 62 of the center valves 60 are separated from the respective cylinder pins 70, i.e. are not supported on the respective cylinder pins 70, the elastic members 64 extend. Due to the extension of the elastic members 64, the center valves 60 are pushed in the communication holes 50 in a backward direction, so that the sealing members 61 come into close contact with the respective valve seats 53.
As a result, the flow of fluid through each communication hole 50 is interrupted, and thus the first and second hydraulic chambers 21 and 31 are closed. Afterwards, due to the continued movement of the first and second pistons 20 and 30, the fluid of each of the first and second hydraulic chambers 21 and 31 is pressed to move to the wheel cylinders.
When the breakage is released, the first and second pistons 20 and 30 are returned to their original positions by the return springs 40, and thereby the valve bodies 62 of the center valves 60 are supported on the cylinder pins 70 again as in FIG. 1.
In this state, the center valves 60 press the respective elastic members 64 in the front thereof, so that the elastic members 64 move forwards in the communication holes 50. Thereby, the sealing members 61 are separated from the respective valve seats 53, and thus the first and second hydraulic chambers 21 and 31 become open.
Meanwhile, this conventional master cylinder is used for applying the braking force to the wheels although the brake is not operated in a brake hydraulic control system, which is equipped with an anti-lock brake system (ABS) for preventing the wheels from locking during braking, a traction control system (TCS) for preventing the drive wheels from excessively slipping when abruptly starting off or accelerating, and an electronic stability program (ESP) for regulating a traveling direction of the vehicle in which a driver wants to go when the traveling direction of the vehicle is not identical to an actual traveling direction of the vehicle as a result of analyzing the state of the steering wheel.
In this manner, when the wheels slip regardless of the operation of the brake pedal, a hydraulic pump draws the fluid of the master cylinder through the first and second outlets 23 and 33, and then pressurizes the drawn fluid again so as to brake the wheels.
However, this conventional master cylinder has a problem in that, because a space where the fluid flows through the communication holes 50 is narrow, the fluid does not smoothly flow from the first and second inflow chambers 24 and 34 to the first and second outlets 23 and 33 through the communication holes 50 when the hydraulic pump draws the fluid of the master cylinder through the first and second outlets 23 and 33.
Further, as illustrated in FIG. 3, an edge 61 a of the sealing member 61 made of rubber is squeezed between the first piston 20 and the valve body 62 of the center valve 60, and thus the sealing member 61 is reduced in durability and sealing efficiency.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.